1. Field of the Invention
The invention relates to a method and to a test bench for testing a starter motor with an electrical dynamometer that is connected to the starter motor and simulates a combustion engine, and a regulator for regulating the electrical dynamometer.
2. The Prior Art
Due to new technologies such as start-stop technology, for example, starter motors for combustion automobiles are subjected to ever-increasing demands, particularly as regards the required number of starting sequences. While 30,000 starting sequences were required 5 years ago, 300,000 starting sequences are already demanded today of starter motors. This necessarily also increases the requirements for the testing of starter motors. Tests on real combustion engines that were previously commonplace can hardly be carried out any more. This is because, on the one hand, at the time of the testing of a starter motor for a new combustion engine or for a new drive train, the latter is oftentimes not even available yet and, on the other hand, the expense of such a test bench is too high, both in terms of costs and time involved, as a result of the necessary media connections and supply lines, e.g., for cooling water, fuel, exhaust, oil, etc., of the combustion engine.
For this reason, test benches for starter motors of combustion engines have already been conceived in which the combustion engine is replaced and simulated by an electrical machine. DE 10 2006 045 973 A1 describes one such test bench. There, the electrical machine is regulated according to a predefinable test characteristic. The test characteristic can be created from measurements on the real combustion engine or from a virtual engine model. However, the test characteristic is then only preset for the respective test run and is removed for every test run, which is repeated 50,000 times, for example.
The problem here is that a system consisting of starter motor and combustion engine does not have an exact deterministic temporal profile. Rather, such an electromechanical system exhibits, within certain limits, a temporally random behavior that can change on the order of magnitude of milliseconds. For example, the timing sequence varies from the point in time of the start signal to the introduction of the starter pinion and until the starter motor builds up the required torque due to the mechanics and electromechanical parts (e.g., relay). Likewise, there can be variations in the timing in the torque generation. As a result, the theoretical characteristic and actual operation are not completely congruent, but rather there can be some time-shifting. For example, if the starter motor is supposed to have already started up according to the test characteristic, i.e., already have a speed of ng, a speed n=0 may still be specified for the dynamometer, which has the effect of a blocking motor. As a result, the starter current would increase greatly, which can lead to unrealistic loads on the starter motor and on the starter pinion and starter ring. Such a test run would not be representative, nor could it be taken into account in testing. What is more, practical experiments have also shown that, as a result of this, damage profiles occur on the starter motor when operating on such a test bench that do not occur in practice. This of course renders such a test bench unusable for real testing of starter motors.
It is therefore the object of the present invention to remedy the above-mentioned problems during the testing of starter motors on test benches using an electrical dynamometer.